Growth of Cubic Boron Nitride/Diamond Heterostructures - Surface Preparation and Film Nucleation
At a Glance
Section titled āAt a Glanceā| Metadata | Details |
|---|---|
| Publication Date | 2023-07-22 |
| Journal | Microscopy and Microanalysis |
| Authors | Saurabh Vishwakarma, Avani Patel, Manuel Roldan Gutierrez, R. J. Nemanich, David J. Smith |
| Institutions | Arizona State University |
| Citations | 3 |
Abstract
Section titled āAbstractāCubic boron nitride (c-BN) is an ultrawide-bandgap (UWBG) semiconductor with many potential applications in high-power and high-temperature devices due to its large bandgap of 6.4 eV, breakdown field greater than 15 MV/cm, and thermal conductivity of ā¼940 W/m.K.However, synthesis of c-BN is challenging since epitaxial growth methods often result in nucleation of metastable phases, namely sp 2 -bonded hexagonal (h-) or sp 3 -bonded wurtzite (w-BN) [1].Our previous study of c-BN growth focused on an in-depth analysis of growth chemistry, substrate type and growth temperature (T s ) in efforts to achieve the cubic phase [2].In this current research, transmission electron microscopy (TEM) and electron-energy-loss spectroscopy (EELS) have been used to evaluate nucleation conditions and different surface preparation methods to further improve the crystal quality and phase purity.The films were grown using electron cyclotron resonance plasma-enhanced chemical vapor deposition (ECR PECVD).Samples suitable for cross-sectional TEM observation were prepared by focused-ion beam (FIB) milling using a Thermo-Fisher Helios 5UX dual-beam instrument with initial thinning at 30 keV and further thinning at 5 keV and 2 keV.A Philips-FEI CM-200 FEG TEM operated at 200 kV and a probe-corrected JEOL ARM200 operated at 200 kV were used for imaging and EELS analysis, respectively.Fig. 1 shows an EELS spectrum analysis across the BN-diamond interface of the sample prepared with H 2 /BF 3 ratios of 0.75 for the initial 44 mins, and 1, for the next 105 mins, with T s = 850 Ā°C.Prior to growth, the diamond substrate was annealed at 830 Ā°C to remove adsorbed oxygen, and then further cleaned with H 2 plasma at 750 Ā°C for 1.5 hrs.Fig. 1(a) shows identical spectrum images that combine EELS data for low-loss energies in the range from 0 to 460 eV.The EELS spectra from the ā¼2-3 nm thick nucleation layer near the interface (B, C, and D) show significant Ļ* peaks at ā¼191 eV, indicating the presence of sp 2 -bonded BN.This undesired nucleation of the sp 2 layer can likely be attributed to defects introduced by the aggressive substrate cleaning procedure.A second sample was prepared with a modified cleaning method, where the substrate was plasma-cleaned for only 10 minutes and a growth duration of 40 minutes with H 2 /BF 3 ratio = 0.75.Fig. 2(a) shows markedly reduced defect density in the substrate and a reduced proportion of w-BN islands at the interface, with no visible h-or t-BN phases.Fig. 2(b) shows a high magnification TEM image of an almost epitaxial c-BN.Further experiments are in progress to identify optimal cleaning and nucleation conditions to yield the pure cubic phase [3].